1. Field of the Invention
The present invention relates to a bias voltage generator circuit for an amplifier. More specifically, it relates to a bias voltage generator circuit capable of keeping a bias voltage constant.
2. Description of the Related Art
Conventionally, what has been known as a circuit arrangement for keeping a circuit current constant with a fixed bias voltage even when a source voltage fluctuates is an arrangement including: a first p-channel field effect having a source connected to a power source; a first n-channel field effect transistor having a drain connected to a drain of the first p-channel field effect transistor; a second p-channel field effect transistor having a source connected to the power source and a gate connected to a gate of the first p-channel field effect transistor and the drain thereof; and a second n-channel field effect transistor having a drain connected to a gate of the first n-channel field effect transistor and through a resistor to a drain of the second p-channel field effect transistor, the second n-channel field effect transistor having a gate connected to the drain of the second p-channel field effect transistor. Also, as shown in FIG. 8, there has been known an arrangement including: a first p-channel field effect transistor MP1000 having a source connected to a power source; a first n-channel field effect transistor MN1000 having a gate and a drain, both connected to a drain of the first p-channel field effect transistor; a second p-channel field effect transistor MP2000 having a source connected to the power source and a drain connected to a gate of the first p-channel field effect transistor MP1000; and a second n-channel field effect transistor MN2000 having a drain connected to a gate of the second p-channel field effect transistor MP2000 and through a resistor R1000 to the drain of the second p-channel field effect transistor MP2000, the second n-channel field effect transistor MN2000 having a gate connected to the gate of the first n-channel field effect transistor MN1000. (See Japanese Unexamined Patent Application Publication No. JP-A-64-42717.)
This type of circuit commonly has a tendency to depend on the size and characteristics of transistors in setting voltage and flatness. Even with the above conventional example, the flatness is increased, but there is still a tendency to depend on a source voltage under the actual characteristics of transistors. Therefore, there has been a problem such that an increase in source voltage increases the bias voltage and the circuit current. The invention has as its object to provide a bias voltage generator circuit, which can solve such conventional problem and keep a constant electric current consumption and supply a bias voltage kept at a constant value relative to its source voltage and a voltage kept at a constant value relative to the ground (GND) potential even when the source voltage fluctuates.